many, many thanks to those of you who pointed out that a hissing (sissing?) 
noise is likely not electrical.  it was not.  nor was it smoke.
we visually checked out all the electrical, which looked ok.
so i opened up the heater control valve all the way, and she started the 
engine.  took a couple of minutes before the "smoke" appeared from under the 
passenger side of the dashboard.  it smelled suspiciously like antifreeze 
and dripped on the carpet.
we've lost either a heater hose (we hope) or the heater core itself.
 
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